Tackle the last of the low hanging fruit for memory allocations in the main game loop.

- Avoid calling string.Split twice in SprintFont.Measure.
- Change ActorsInBox method of ActorMap and ScreenMap to avoid allocating and intermediate list. As a bonus this allows the sequence to be lazily consumed. Also avoid LINQ in these methods.
- In FrozenUnderFog.TickRender, the method exits early if no players are visible so the attempt at lazy generation was not needed.
- Unwrap a LINQ Any call in ClassicProductionQueue.Tick.
- Merge some successive Where calls in ProximityCapturable into single predicates.
Merge pull request #5679 from RoosterDragon/main-loop-alloc

Reduce memory allocation in the main loop
Merge branch 'bleed' of https://github.com/OpenRA/OpenRA into bleed